Electronic circuit arrangements for converting an input voltage signal having a first voltage level into an output voltage signal having a second voltage level are known. Conventional electronic circuit arrangements of this type permit input voltage signals having a wide input voltage range of 80 V to 300 V, for example, to be converted into corresponding output voltage signals. In order that the electronic circuit arrangement can process voltage signals having such a wide input voltage range, the input of the electronic circuit arrangement must have a high-impedance input, that is to say that the electronic circuit arrangement must have a high input impedance relative to the input voltage signal to be processed or to be amplified.
The solution proposed in the prior art for processing input voltage signals in a wide input voltage range has numerous disadvantages, however. One essential disadvantage of conventional circuit arrangements is that high input impedances result in the circuit arrangement having a high susceptibility to interference. High-impedance inputs are extremely sensitive in particular toward crosstalk between channels, cross-modulation effects, noise and interference induced by electrical and magnetic fields.
In many cases, however, it is absolutely necessary to identify without interference a change in a level of an input voltage signal to be processed, for example when a switch-on instant is to be detected precisely. This is of great importance particularly when detecting digital or binary signals. Such digital or binary signals, too, can have a large input voltage range, as specified above, in different applications.
In order to improve the interference immunity of conventional electronic circuit arrangements, it has been proposed in the prior art to reduce the input impedance of such electronic circuit arrangements. This leads to high currents and thus to high power losses in an inexpedient manner in the case of the input voltage ranges considered (80 V-300 V). Although the reduction of the input impedance lessens somewhat the sensitivity to the abovementioned disturbing interference, such as, for example, crosstalk, cross-modulation, noise components, interference induced by electrical or magnetic fields, and the problem associated with electromagnetic compatibility, the increase in the power loss on account of the increased input current at a lower input impedance cannot be tolerated for many applications.